The use of gantry presses is now common for the manufacture of prefabricated truss structures. The remote prefabrication of truss structures, including roof and floor trusses, for later transport to the job site for assembly into a building or other structure under construction is a well known practice which, due to greater efficiency, provides a significant time and labour requirement savings compared to job site assembly.
As will be understood by the skilled person, the remoter prefabrication of truss structures includes the assembly of truss members, such as chord and other web members, on a truss assembly table. The truss members have generally top and bottom surfaces and the truss members are laid out on the work surface of the truss assembly table, typically in a predetermined pattern or arrangement, according to the size and shape of the truss assembly desired to be prefabricated. The truss members are coupled by connector plates with toothed or nail-like protrusions, the connector plate protrusion being on one side of the plate. In assembly of the truss members into the desired truss assembly, size and shape, the connector plates are positioned where truss members abut, so the protrusions may be embedded in the truss members.
A gantry type press machine is typically used to imbed the connector plates into the truss members, to manufacture the truss assembly. Connector plates will typically be embedded in first one surface of the members of the truss assembly, the truss assembly then flipped on the surface of the truss assembly table, and connector plates imbedded in the other surface of the truss assembly.
Typically, a truss assembly manufacturing facility includes a truss assembly table and a gantry type press machine, such as a press roller, which moves relative to the work surfaces of the truss assembly table, the press roller applying pressure to imbed connector plates into the truss members.
The length of required work surface of a truss assembly table will vary with the length of truss assembly to be fabricated.
For a shorter truss assembly, a single assembly table may be used. For a longer truss assembly, it is typical to use a single long truss assembly table, with regular spaces along the length of the table to define sections of the table, or a line of tables in a row with spaces between the tables, arranged to permit access to worker between tables or table sections, to permit easier access to workers to the work surface of the assembly table, for handling of the truss members, connector plates and the assembled truss.
Various types of truss assembly gantries and like apparatus are well known in the art, for assembly of truss structures remote from the job site and for use in methods of such assembly.
U.S. Pat. No. 3,667,379 and U.S. Pat. No. 3,925,870 are examples of apparatuses for the two-step penetration and installation of truss plates onto wooden truss elements, with a fixed pressing station and the truss elements assembled on a moving table or surface.
U.S. Pat. No. 4,295,269 and U.S. Pat. No. 4,437,234 are examples of truss assembly machines wherein the press roller is mounted on a moveable presser carriage, coupled and supported by the truss assembly table for reciprocating movement. In such assemblies, the presser carriage, moves by rolling contact between the press roller itself and a table member, such as a rail extending the length of the table. The press roller, by direct contact with the table rail moves along the length of the table functioning to press connector plates into the joints of truss elements positioned on the table. Rotating bearings coupled to the present carriage engage a side beam extending the length of the table, to constrain lateral and upward movement of the presser carriage.
Another known design of truss assembly apparatus is where the gantry carriage straddles the work table, moving along the work surface, supported on rails secured to the floor of the work area containing the truss assembly apparatus. Such rails are positioned adjacent and parallel to either side of the truss assembly table, for movement and support of the truss assembly gantry or like apparatus along the length of the truss assembly table work surface. Examples of the above type of truss assembly apparatus may be found in U.S. Pat. No. 5,933,958, U.S. Pat. No. 4,084,498, U.S. Pat. No. 5,048,409 and U.S. Pat. No. 5,211,108.
The above mentioned truss assemblies all exhibit certain drawbacks for the manufacture of pre-fabricated trusses. The assembly of trusses of larger dimension and of certain configurations may be more complex where truss assembly apparatuses with a moving table are used. As well, a truss assembly apparatus with a fixed floor rail for support of the truss assembly gantry may pose a tripping hazard to assembly workers attempting to access the surface of the truss assembly table.
Press roller assemblies without floor rails, such as those described in U.S. Pat. No. 4,295,269 or U.S. Pat. No. 4,437,234 still restrict access to the surface of the work table.
More recently, as truss assembly tables and work surfaces have become wider and longer for the purpose of assembling trusses of larger dimension, and otherwise generally to facilitate worker access to the truss members and truss connector plates, truss assembly apparatuses have been designed with regular spaces in the truss table work surface or with separate tables spaced by being positioned in a line as described above, allowing access to the worker to the spaces there between. Truss assemblies where the gantry is mounted on a floor rail system will again impede access by the worker to the spaces between sections of the working surface of the truss assembly table. Likewise, truss assembly designs with spaced work surfaces and table mounted rails for support and reciprocating movement of the press gantry across the spaces adjacent work surfaces will impede worker access to the spaces between work surface sections.
Table mounted rail assemblies typically include wheel or bearing assemblies rotatably mounted to the gantry assembly, for reciprocating movement of the gantry assembly along the table work surfaces. Such designs have the drawback of limiting the points of contact between the gantry assembly and the table mounted rails to permit the gantry assembly to traverse the space between work surfaces by engaging only one of the work table surfaces.
Additionally, table mounted wheel or bearing gantry assemblies will result in greater machinery vibration being transferred to the work surface, as compared to floor rail mounted gantry assemblies, making more difficult the proper assembly of truss elements and connector plates.
Additionally, truss assemblies with table mounted rails will require means to constrain lateral and upward movement of the gantry assembly relative to the rails and work surface. Typically, this may be by a bearing or wheel assembly, rotatably mounted on the gantry assembly. In an emergency where very quick stoppage of the apparatus is required, because of the rotating bearings, such assemblies may not be able to stop swiftly enough due to momentum of the apparatus, thereby still posing a safety hazard to the worker.
Accordingly, there is a requirement for a gantry type truss assembly apparatus without floor rails for mounting and movement of the truss assembly gantry. For truss assembly table designs with spacing between work sections, there is also a requirement for a truss assembly apparatus which does not restrict access to the worker to the space between work sections and where the gantry may move on a table mounted rail without the rails restricting access to the spaces between table sections, to the worker. Further, there is a requirement for a table mounted rail assembly which limits machine vibrations transfer to the work surface, while permitting movement of the gantry assembly across, the space between work surfaces, supported by only one of the table work surfaces. Additionally, a gantry type truss assembly is desired with greater security in circumstances where an emergency stoppage of the relative movement of the gantry assembly to the table is required.